Volunteers are assigned to 1 of 4 groups. Volunteers in Groups A, B, and C take a statin (simvastatin, atorvastatin, or pravastatin, respectively) on Days 0 to 3. After Day 3, the statin is stopped and EFV is begun. Volunteers take EFV until Day 14 and the statin and EFV together from Days 15 to 18. Volunteers in Group D take pravastatin on Days 0 to 3, NFV on Days 4 to 12, and pravastatin and NFV together on Days 13 to 16. Fasting lipid profiles are performed on Days 0, 4, 15, and 19 for Groups A, B, and C, and on Days 0, 3, 13, and 16 for Group D. PK sampling is performed on Days 3, 14, and 18 for Groups A, B, and C (requiring an overnight stay), and on Days 3 and 16 for Group D. Volunteers receive monetary compensation for participation in this study.